sed like replace syntax replaces all occurences

Description

When you use sed like syntax to replace a part of message, all occurences are being replaced.

Steps to reproduce

1. Write a test message
2. Write a s/t/b/

What is the current bug behavior?

The resulting message would be besb

What is the expected correct behavior?

The resulting message should be best. If we want to replace all occurences of t, we should've used s/t/b/g

Relevant logs and/or screenshots

(Paste any relevant logs - please use code blocks (```) to format console output, logs, and code, as it's very hard to read otherwise.)

Possible fixes

(If you can, link to the line of code that might be responsible for the problem)

System/Matrix Information

• Distribution / Platform: Archlinux
• Qt Version: 5.15.2
• NeoChat version: 1.2
• Quotient version: 0.6.6
• Matrix server: wvffle.net